1. Field of the Invention
The present invention relates to a lens barrel which incorporates a one-way rotational transfer mechanism.
2. Description of the Related Art
Among conventional lens barrels available for both autofocus (AF) and manual focus (MF), a lens barrel including a stationary ring, a movable ring, a distance adjustment ring, and an AF motor and a manual focus ring, wherein the movable ring is concentrically arranged with the stationary ring, supports a focusing lens group and is movable forward and rearward along an optical axis, wherein the distance adjustment ring is concentrically arranged with the stationary ring and rotates on an axis of the distance adjustment ring to move the movable ring forward and rearward along the optical axis, wherein the AF motor drives the distance adjustment ring, and wherein the manual focus ring is manually rotated about its axis to rotate the distance adjustment ring, is known in the art.
Such a conventional lens barrel is disclosed in, e.g., Japanese Unexamined Patent Publication H02-253214 and Japanese Unexamined Patent Publication H02-253210.
In the lens barrel disclosed in Japanese Unexamined Patent Publication H02-253214, the manual focus ring rotates while an autofocusing operation is performed because a driving force of an AF motor is transferred to the manual focus ring during the autofocusing operation. Accordingly, the autofocusing operation is not performed smoothly if the user touches their hand on the manual focus ring during the autofocusing operation.
On the other hand, in the lens barrel disclosed in Japanese. Unexamined Patent Publication H02-253210, although the manual focus ring does not rotate even if a driving force of an AF motor is transferred to the manual focus ring during the autofocusing operation, the manual focus ring cannot be easily rotated manually because a predetermined load is continuously applied to the manual focus ring so that the manual focus ring cannot rotate by the driving force of the AF motor during the autofocusing operation.
In addition, among the aforementioned conventional lens barrels usable for both autofocus (AF) and manual focus (MF), a lens barrel which incorporates a one-way rotational transfer mechanism between the distance adjustment ring and an AF motor, wherein a torque of the distance adjustment ring rotated by a rotation of the manual focus ring is not transferred to the AF motor when the manual focus ring is manually rotated even though a driving force of the AF motor is transferred to the distance adjustment ring when the AF motor is driven, is known in the art.
This type of lens barrel is disclosed in e.g., Japanese Unexamined Patent Publication H11-202181. In this type of lens barrel, a manual focusing operation can be carried out even in AF mode with an AF switch remained ON.
However, in the lens barrel disclosed in Japanese Unexamined Patent Publication H11-202181, there is a possibility of the one-way rotational transfer mechanism becoming incapable of securely transferring torque from the. AF motor to the distance adjustment ring to thereby make it impossible to perform an autofocusing operation when the AF motor is driven.